The present invention relates to heat sensitive devices and, more particularly, to a heat sensitive cable and method of making same.
Heat sensitive cables which are characterized by the use of semiconductive materials having inverse temperature-resistance characteristics in conjunction with dissimilar thermoelectric conductors are now well known in the art. Such cables are particularly suitable where it is desired to monitor the greatest temperature existing along the length of the cable, and are exemplified in connection with a system for measuring and locating temperature conditions of interest in U.S. Pat. Nos. 3,408,607 and 4,324,138. Thermistor cables which are characterized by a core of semiconductive material surrounded by a mass of temperature-resistant electrically-insulating material covered with a protective metallic sheath are also well known in the art.
Despite the clear advantages and many applications for such cables, they have simply not evolved to the point of providing the desired degree of versatility. It has remained to develop a heat sensitive cable capable of generating a measurable and predictable voltage when the entire length of cable is at ambient, e.g., 72.degree. F., wherein the cable is also adapted to provide a change in the temperature representative measurable voltage with an increase in temperature above the prevailing ambient at any location along the cable. If this could be achieved with an electrical insulation having a negative temperature coefficient, the thermoelectric output of the cable or a section thereof would be altered in a predictable fashion.
Moreover, if this could be achieved, the cable location where an increase in temperature takes place could be located electronically. This could be done, for instance, as fully disclosed and claimed in my earlier U.S. Pat. No. 4,324,138, issued Apr. 13, 1982, for a method of and apparatus and system for determining temperature conditions. As set forth therein, the applications are virtually limitless.
While the value of heat sensitive cable has long been recognized, it has remained to provide such a cable having the requisite versatility for the many applications to be benefited by use thereof. In fact, despite my many prior inventions in this field, as exemplified by U.S. Pat. Nos. 3,408,607 and 3,513,432, the missing link to providing a highly versatile cable has remained. Despite the advantages that will be recognized by those skilled in the art, heat sensitive cable which may not only be utilized to monitor ambient temperature but also may be utilized to monitor for any localized increase above ambient temperature has simply not been available.
It is therefore an object of the present invention to provide a heat sensitive cable having means for generating a temperature representative measurable voltage.
It is also an object of the present invention to provide a cable of the type described utilizing a pair of thermoelectric conductors disposed in contacting side-by-side relation together with means for passively self-generating a temperature representative measurable voltage between the conductors when the cable is exposed to ambient temperature.
It is a further object of the present invention to provide a cable of the type described utilizing a flexible outer jacket formed of an electrically non-conductive material to completely surround the conductors.
It is another object of the present invention to provide a cable of the type described which is not only passive and self-generating to generate a voltage potential between the thermoelectric conductors indicative of the temperature existing along the entire length of the cable, i.e., the ambient temperature, but which also generates a voltage potential between the conductors indicative of the hottest point along the length of the cable if the temperatures are unequal.
It is still another object of the present invention to provide a cable of the type described in which the passive self-generating characteristic causes a change in the temperature representative measurable voltage with an increase or decrease in temperature at every location along the jacket.
It is still another object of the present invention to provide a cable of the type described in which the passive self-generating characteristic causes a change in the temperature representative measurable voltage with an increase in temperature above the prevailing ambient at any location along the jacket.
It is still another object of the present invention to provide a cable of the type described capable of precise, nonperishable, reproducible measurement of the temperature and identification of the location of the hottest spot when monitoring with a high input impedance temperature device.
It is another object of the present invention to provide a cable of the type described wherein the outer jacket and the thermoelectric conductors can be formed of various materials and combinations of materials to yield various mechanical properties and temperature-voltage response curves.
It is a further object of the present invention to provide a cable of the type described which can be produced in lengths of thousands of feet at a fraction of the cost of making other types or constructions of heat sensitive cable.
An additional object of the present invention is to provide a cable of the type described utilizing commercially available materials and processes to manufacture the cable.
These and other objects, advantages and features of the present invention will be apparent from a consideration of the accompanying specification, claims and drawings.